On Thu, Apr 25, 2019 at 04:35:48PM +0100, Dave Martin wrote: > On Thu, Apr 25, 2019 at 08:14:52AM -0700, Yu-cheng Yu wrote: > > On Thu, 2019-04-25 at 12:02 +0100, Dave Martin wrote: > > > On Mon, Nov 19, 2018 at 01:48:05PM -0800, Yu-cheng Yu wrote: > > > > Look in .note.gnu.property of an ELF file and check if Shadow Stack needs > > > > to be enabled for the task. > > > > > > What's the status of this series? I don't see anything in linux-next > > > yet. > > > > > > For describing ELF features, Arm has recently adopted > > > NT_GNU_PROPERTY_TYPE_0, with properties closely modelled on > > > GNU_PROPERTY_X86_FEATURE_1_AND etc. [1] > > > > > > So, arm64 will be need something like this patch for supporting new > > > features (such as the Branch Target Identification feature of ARMv8.5-A > > > [2]). > > > > > > If this series isn't likely to merge soon, can we split this patch into > > > generic and x86-specific parts and handle them separately? > > > > > > It would be good to see the generic ELF note parsing move to common > > > code -- I'll take a look and comment in more detail. > > > > Yes, I will work on that. > > Thanks. I may try to hack something in the meantime based on your > patch. > > One other question: according to the draft spec at > https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI, it > looks like the .note.gnu.property section is supposed to be marked with > SHF_ALLOC in object files. > > I think that means that the linker will map it with a PT_LOAD entry in > the program header table in addition to the PT_NOTE that describes the > location of the note. I need to check what the toolchain actually > does. > > If so, can we simply rely on the notes being already mapped, rather than > needing to do additional I/O on the ELF file to fetch the notes? [...] BTW, it looks like this holds true for AArch64 (see below). Providing this also works on other arches, I think we can just pick PT_GNU_PROPERTY out of the program headers and rely on the corresponding note being already mapped by the existing binfmt_elf code. Cheers ---Dave --8<-- $ echo 'void f(void) { }' | \ aarch64-linux-gnu-gcc -v -nostdlib -Wl,-ef \ -mbranch-protection=standard -o /tmp/x -x c - && \ aarch64-linux-gnu-readelf -nl /tmp/x [...] gcc version 9.0.1 20190425 (experimental) (GCC) [...] GNU assembler version 2.32.51 (aarch64-linux-gnu) using BFD version (GNU Binutils) 2.32.51.20190425 [...] Elf file type is EXEC (Executable file) Entry point 0x400178 There are 5 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flags Align LOAD 0x0000000000000000 0x0000000000400000 0x0000000000400000 0x00000000000001c0 0x00000000000001c0 R E 0x10000 NOTE 0x0000000000000158 0x0000000000400158 0x0000000000400158 0x0000000000000020 0x0000000000000020 R 0x8 GNU_PROPERTY 0x0000000000000158 0x0000000000400158 0x0000000000400158 0x0000000000000020 0x0000000000000020 R 0x8 GNU_EH_FRAME 0x0000000000000184 0x0000000000400184 0x0000000000400184 0x0000000000000014 0x0000000000000014 R 0x4 GNU_STACK 0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000 RW 0x10 Section to Segment mapping: Segment Sections... 00 .note.gnu.property .text .eh_frame_hdr .eh_frame 01 .note.gnu.property 02 .note.gnu.property 03 .eh_frame_hdr 04 Displaying notes found in: .note.gnu.property Owner Data size Description GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0 Properties: AArch64 feature: BTI, PAC
